28-05-2025
Tend to feel sad in winter? It might be in your genes
Feeling sad in the winter could be caused by your genetics, a study suggests.
Seasonal affective disorder (SAD) affects around one in 20 people in the UK and leads to low mood and other mental health issues in the colder, darker months.
Now researchers at the University of Michigan have discovered a gene – SLC20A2 – which makes some people even more susceptible to the condition.
The study of more than 3,000 shift workers, who wore Fitbit-style activity trackers, revealed that how well they coped with changes to their daily schedule across the seasons showed correlation with differences in their genes.
Dr Ruby Kim, assistant professor of mathematics at the University of Michigan and study author, said: 'Humans really are seasonal, even though we might not want to admit that in our modern context.
'Day length, the amount of sunlight we get, it really influences our physiology.
'The study shows that our biologically hardwired seasonal timing affects how we adjust to changes in our daily schedules.'
The finding that circadian rhythm was linked to seasonal mood adds credence to the belief that seasonal depression is, to some extent, hardwired into our DNA.
'For some people they might be able to adapt better, but for other people it could be a whole lot worse,' said Prof Daniel Forger, director of the Michigan Center for Applied and Interdisciplinary Mathematics.
The SLC20A2 gene has been seen in animal studies to be linked to seasonality, and the team is now preparing further investigations into how this gene impacts humans.
'We found significant differences in daily steps, time awake, and heart rate-sleep misalignment throughout the year across different genotypes, grouped by polymorphisms [differing characteristics] of the SLC20A2 gene,' the scientists write in their study.
'We see much larger differences in heart rate-sleep misalignment between the genotype groups in the winter than in the summer.
'Based on these findings, we hypothesise that SLC20A2 influences photoperiodic encoding [reaction to day length] in humans.'
The scientists think it is possible this gene 'may be involved in seasonal timing in humans' and could dictate if a person struggles with night shifts or can manage them well.
'We do not think that SLC20A2 alone can explain differences in seasonal behaviours and shift work adaptation, but it may contribute as one of many genetic factors influencing inter-individual variability,' the authors write.
Prof Forger added: 'Brain physiology has been at work for millions of years trying to track dusk and dawn.
'Then industrialisation comes along in the blink of evolution's eye and, right now, we're still racing to catch up.'
